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Best Practices, Breaking in, Trip-Free, and More Discussed at Circuit Breaker Expert Panel

Best Practices, Breaking in, Trip-Free, and More Discussed at Circuit Breaker Expert Panel

With about 170 people attending two Circuit Breaker Panel sessions at PowerTest, one message is clear: Technicians are hungry for insightful information about how to do their jobs better and safer.

At the panel discussions, Group CBS CEO and host Finley Ledbetter was joined by panelists Denise Green (Circuit Breaker Sales, Detroit Apparatus Center), Craig Archer (Western Electrical Services, a Group CBS company), and Robert Foster (Megger). Discussions were lively and the audience was engaged as Finley and crew delved into the biggest circuit breaker trends. Here’s are some of the highlights from the two panel discussions:

Improper lubrication leads to breaker failure, but what’s best practice? Most types of circuit breakers should be maintained every three years, with a maximum of five years. The biggest failure of circuit breakers relates to lubrication, which is very difficult to do in the field because technicians can’t take the breaker apart. A light penetrating oil like WD-40 might wash out the lubrication. The moral of the story: To ensure proper lubrication, circuit breakers need to be disassembled and properly serviced in the shop.

Why trip-free operation matters. Trip-free operation is an ideal characteristic for medium-voltage circuit breakers because it will trip (open) even if the operating mechanism (ON-OFF switch) is held in the ON position. A non-trip-free circuit breaker can be reset and/or held ON, even if an overload or excessive heat condition is present. Lively discussion centered around how IEC breakers’ failure to have this functionality puts them at a disadvantage.

Keep your hands to yourself (and stay away from the finger cluster). Never turn a breaker by grabbing its finger cluster. Breakers are heavy and fingers look like handles, but they’re not. It’s critical that the finger cluster avoids being bent and stays in perfect shape.

Behold the power of the interlock. Drawout circuit breakers use interlocks, which are critical to keep technicians safe while they maintain the breakers. But these don’t completely solve the problem. Consider remote racking and remote switching solutions to fully mitigate arc-flash risks. An all-too-common issue is trying to insert the wrong breaker into the cubicle and defeating or damaging the interlocks.

Best DLRO practices. A digital low resistance ohmmeter (DLRO) verifies if contact resistance readings are within the manufacturer’s technical specification. This testing is easy to do in the shop but not as easy in the field because of the possible need to adjust contact pressure and alignment of the finger clusters. Contact resistance of a 4,000 A 480 V breaker in good condition should be less than 30 microohms. It was suggested to use a 100 A DLRO if testing with a 10 A DLRO failed.

The first trip test is critical. There should be 2 ms maximum in variation between the three phases of a medium-voltage breaker. Open and close time should also be balanced within 2 ms. The same goes for vacuum contactors/starter. Furthermore, over-travel and rebound issues indicate future issues with your electrical equipment.

Test and maintain older breaker spares. Spares for older breakers such as the Type DS — designed specifically for use in metal-enclosed low-voltage switchgear up to 600 V AC — that have been out of service for a long time can have lubrication issues or high contact resistance. Spares need maintenance and should always be tested before performing maintenance on in-service breakers. This ensures availability should they needed to replace a malfunctioning in-service breaker.

Extend life of vacuum interrupters. With parts built overseas, new vacuum breakers won’t last as long as previous generations. In a separate session at PowerTest, Finley presented a paper on reconditioning and extending the life of certain vacuum interrupters.

Establish a schedule for high-current primary injection testing. A high-current primary injection test, which verifies the overall proper functioning of a circuit breaker and its trip device, should be performed on brand-new circuit breakers before putting them in service. Complete a secondary injection test of breakers with static trip devices at three years, and a primary injection test again at five or six years maximum.

The key to success: Always communicate. In the end, good communication between the service company and the customer can prevent many of the headaches associated with circuit breaker testing and maintenance. For example, if the service company doesn’t communicate what it will be doing and what it will need, the customer might have all the breakers pulled out of the switchgear before the testing company is on the job site. This makes first-trip testing impossible. Other helpful tips: The testing company should report deficiencies to the customer right away and provide a comprehensive test report within two weeks.

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